Transverse load optimization in Nb3Sn CICC design; influence of cabling, void fraction and strand stiffness
Transverse load optimization in Nb3Sn CICC design; influence of cabling, void fraction and strand stiffness
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DOI：
10.1088/0953-2048/19/9/011
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发表时间：
2006-07
影响因子：
3.6
通讯作者：
A. Nijhuis;Y. Ilyin
中科院分区：
文献类型：
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作者：
A. Nijhuis;Y. Ilyin
我们开发了一个模型，根据绞线和电缆特性描述 Nb3Sn CICC 的横向载荷退化，并且能够预测如何防止这种退化。国际热核实验反应堆 (ITER) 导管导体 (CICC) 中的 Nb3Sn 电缆的性能随着电磁负载的增加而显着下降。复合材料热收缩的差异不仅会影响临界电流和温度裕度，而且大部分电磁力会在 Nb3Sn 层中引起显着的横向股线接触和弯曲应变。在这里，我们提出了横向电磁负载优化 (TEMLOP) 模型，并根据用于环形场模型线圈 (TFMC) 的内部锡绞线的测量特性，报告了 ITER 类型导体的第一个计算结果。作为输入，该模型使用描述单股线在周期性弯曲和接触载荷下的行为的数据，并通过 TARSIS 设置进行测量，从而能够区分每种特定负载和股线类型的性能降低。模型计算最重要的结论是，通过增加后续布线阶段的间距长度，可以彻底、直接地改善大型CICC严重退化的问题。这是第一次提出增加螺距，目前还没有可用的实验数据来证实 TEMLOP 模型的这一有益结果。较大的节距长度将通过显着缓和与中等长度绞合节距相关的局部峰值应力而导致电缆中的应力和应变分布更均匀。不幸的是，当前导体布局的扭曲节距方案接近于最坏情况。该模型还清楚地表明，线束弯曲是导致降解的主要机制。股线交叉和线接触上的横向载荷（简称为接触载荷）局部可达到 90 MPa，但这发生在导体的低场区域，并且在观察到的临界电流衰减中不起重要作用。该模型准确地描述了绞线对电缆中逐层横向载荷的机械响应，与在电缆上进行的机械实验一致。主要通过改变布线方案来改善 ITER 导体设计或运行裕度是可能的。我们还发现，较低的电缆空隙率和较大的绞线刚度有助于进一步提高导体性能。
We have developed a model that describes the transverse load degradation in Nb3Sn CICCs, based on strand and cable properties, and that is capable of predicting how such degradation can be prevented. The Nb3Sn cable in conduit conductors (CICCs) for the International Thermonuclear Experimental Reactor (ITER) show a significant degradation in their performance with increasing electromagnetic load. Not only do the differences in the thermal contraction of the composite materials affect the critical current and temperature margin, but mostly electromagnetic forces cause significant transverse strand contact and bending strain in the Nb3Sn layers. Here, we present the model for transverse electro-magnetic load optimization (TEMLOP) and report the first results of computations for the ITER type of conductors, based on the measured properties of the internal tin strand used for the toroidal field model coil (TFMC). As input, the model uses data describing the behaviour of single strands under periodic bending and contact loads, measured with the TARSIS set-up, enabling a discrimination in performance reduction per specific load and strand type. The most important conclusion of the model computations is that the problem of the severe degradation of large CICCs can be drastically and straightforwardly improved by increasing the pitch length of subsequent cabling stages. It is the first time that an increase of the pitches has been proposed and no experimental data are available yet to confirm this beneficial outcome of the TEMLOP model. Larger pitch lengths will result in a more homogeneous distribution of the stresses and strains in the cable by significantly moderating the local peak stresses associated with the intermediate-length twist pitches. The twist pitch scheme of the present conductor layout turns out to be unfortunately close to a worst-case scenario. The model also makes clear that strand bending is the dominant mechanism causing degradation. The transverse load on strand crossings and line contacts, abbreviated as contact load, can locally reach 90 MPa but this occurs in the low field area of the conductor and does not play a significant role in the observed critical current degradation. The model gives an accurate description for the mechanical response of the strands to a transverse load, from layer to layer in the cable, in agreement with mechanical experiments performed on cables. It is possible to improve the ITER conductor design or the operation margin, mainly by a change in the cabling scheme. We also find that a lower cable void fraction and larger strand stiffness add to a further improvement of the conductor performance.